org.das2.qds.math.fft.jnt

Class RealDoubleFFT

java.lang.Object

org.das2.qds.math.fft.jnt.RealDoubleFFT

Direct Known Subclasses:

RealDoubleFFT_Even

public abstract class RealDoubleFFT
extends java.lang.Object

Abstract Class representing FFT's of real, double precision data. Concrete classes are typically named RealDoubleFFT_method, implement the FFT using some particular method.

The physical layout of the mathematical data d[i] in the array data is as follows:

    d[i] = data[i0 + stride*i]

The FFT (D[i]) of real data (d[i]) is complex, but restricted by symmetry:

    D[n-i] = conj(D[i])

It turns out that there are still n `independent' values, so the transformation can still be carried out in-place. However, each Real FFT method tends to leave the real and imaginary parts distributed in the data array in its own unique arrangment.

You must consult the documentation for the specific classes implementing RealDoubleFFT for the details. Note, however, that each class's backtransform and inverse methods understand thier own unique ordering of the transformed result and can invert it correctly.

Constructor Summary

Constructors

Constructor and Description
RealDoubleFFT(int n) Create an FFT for transforming n points of real, double precision data.

Method Summary

Modifier and Type	Method and Description
void	backtransform(ComplexArray.Double data) Compute the (unnomalized) inverse FFT of data, leaving it in place.
abstract void	backtransform(ComplexArray.Double data, int i0, int stride) Compute the (unnomalized) inverse FFT of data, leaving it in place.
protected void	checkData(double[] data, int i0, int stride)
void	inverse(ComplexArray.Double data) Compute the (nomalized) inverse FFT of data, leaving it in place.
void	inverse(ComplexArray.Double data, int i0, int stride) Compute the (nomalized) inverse FFT of data, leaving it in place.
double	normalization() Return the normalization factor.
void	transform(ComplexArray.Double data) Compute the Fast Fourier Transform of data leaving the result in data.
abstract void	transform(ComplexArray.Double data, int i0, int stride) Compute the Fast Fourier Transform of data leaving the result in data.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

RealDoubleFFT

public RealDoubleFFT(int n)

Create an FFT for transforming n points of real, double precision data.

Method Detail

checkData

protected void checkData(double[] data,
                         int i0,
                         int stride)

transform

public void transform(ComplexArray.Double data)

Compute the Fast Fourier Transform of data leaving the result in data.

transform

public abstract void transform(ComplexArray.Double data,
                               int i0,
                               int stride)

Compute the Fast Fourier Transform of data leaving the result in data.

backtransform

public void backtransform(ComplexArray.Double data)

Compute the (unnomalized) inverse FFT of data, leaving it in place.

backtransform

public abstract void backtransform(ComplexArray.Double data,
                                   int i0,
                                   int stride)

Compute the (unnomalized) inverse FFT of data, leaving it in place.

normalization

public double normalization()

Return the normalization factor. Multiply the elements of the backtransform'ed data to get the normalized inverse.

inverse

public void inverse(ComplexArray.Double data)

Compute the (nomalized) inverse FFT of data, leaving it in place.

inverse

public void inverse(ComplexArray.Double data,
                    int i0,
                    int stride)

Compute the (nomalized) inverse FFT of data, leaving it in place.